A pinned creature is tightly bound and can take few actions. A pinned creature cannot move and is flat-footed.
A pinned character also takes an additional –4 penalty to his Armor Class.
A pinned creature is limited in the actions that it can take. A pinned creature can always attempt to free itself, usually through a combat maneuver check or Escape Artist check.
A pinned creature can take verbal and mental actions, but cannot cast any spells that require a somatic or material component. A pinned character who attempts to cast a spell must make a concentration check (DC 10 + grappler’s CMB + spell level) or lose the spell.
Pinned is a more severe version of grappled, and their effects do not stack.